Method of electroplating copper on metal articles



MTH, in

Jan. 26, 1954 G. E. MURRAY METHODS OF ELECTROPLATING COPPER ON METAL ARTICLES Filed June 5, 195o /NVE/VTOR 6'. E. MURRAY ArrRA/Ev Patented Jan. 26, 1954 METHOD OF ELECTROPLATING COPPER ON METAL ARTICLES Guy E. Murray, Towson, Md., assgnor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application June 3, 1950, Serial No. 165,985

11 Claims.

This invention relates to methods of electroplating copper on metal articles, and more particularly to methods of electroplatng conductive layers of copper on steel wires.

In the manufacture of composite conductors including a steel core and a conductive copper covering enclosing the steel core, it has been proposed in the past to form the copper covering by electrodeposition upon the steel core. However, in the prior art methods it has been impossible to produce economically a composite conductor including steel Wire having a thick, line-grained, nonporous, copper covering, because whenever the current densities used on the core were sufficiently high to make the electroplating process economically feasible, the resulting coverings were coarse-grained and generally unsatisfactory.

An object of the invention is to provide new and improved methods of electroplating copper on metal articles.

A further object of the invention is to provide new and improved methods of electroplating copper on steel wires.

Another object of the invention is to provide new and improved methods of electroplating tenaciously adherent, line-grained, nonporous, thick copper coverings on steel cores at high rates of speed.

An additional object of the invention is to provide new and improved methods of electroplating heavy, electroconductive layers of copper on high strength steel wires to produce composite conductors suitable for use in communication systems, and the like.

A method illustrating certain features of the invention may include electroplating a very thin, line-grained, copper flash deposit on a metal article in an alkaline bath having a predetermined low copper concentration therein, electroplating a heavier, protective deposit of copper on the line-grained deposit in a second alkaline bath having a concentration of copper therein substantially greater than that in the first-mem tioned bath, and then electroplating a heavy deposit of copper on the article in an acid copper plating bath.

A complete understanding of the invention may be obtained from the following detailed description of a method forming a specic embodiment thereof, when read in conjunction with the appended drawing, in which:

Fig. l is a schematic view of an apparatus for practicing a method forming one embodiment of the invention, and

Fig. 2 is a longitudinal, vertical section oi a ,copper plating cell forming a, portion of the apparatus shown in Fig. 1.

A Wire l0 composed of high tensile strength, high carbon steel is withdrawn from a supply Ii thereof by a capstan I2. In order to prepare the wire for electroplating copper thereon, it is advanced continuously by the capstan I2 through a degreaser Iii, which applies trichloroethylene or other suitable degreasing solvent, to the wire to remove grease therefrom. The wire then passes successively through an alkaline electrolytic cleaning cell I5, which cleans the surface of the wire, a water rinsing bath I6, which washes the alklaine material from the surface of the wire, an acid electrolytic cell Il, which preferably contains sulphuric acid and further cleans the surface of the wire I, and a water rinsing bath I8, which rinses the acid from the wire.

The cell I5 preferably contains an electrolyte consisting of a water solution of sodium orthosilicate having a, concentration of from about 3.0 to about 7.0 ounces per gallon of water. The electrolyte in the cell I5 is kept at a temperature within the range of from about 140 F. to about 200 F. Positive contact sheaves lil- I9 which engage the wire Ill and a suitable cathode 20 cause an electric current to flow through the wire and the electrolyte in the cell I5. The current density on the Wire in the cell I5 is maintained at a value within the range of from about 50 to about 200 amperes per square foot.

The cell il preferably contains an electrolyte composed of a sulphuric acid solution having a concentration of from about 5% `to about 25%, and the electrolyte is maintained at a temperature below F. Positive contact sheaves ZI-2I in engagement with the wire I and a cathode 22 cause an electric current to flow through the Wire and the electrolyte at a current density on the wire from about 400 to about 1000 amperes per square foot.

The degreaser I4, the cells I5 and Il and the baths i6 and I8 clean the surface of the wire I0 thoroughly so that the wire is very smooth and clean. The wire then is advanced as a cathode through a ash plating cell 24 having a loW copper concentration, alkaline cyanide electrolyte to apply a very line-grained, thin ilash deposit on the wire. This thin copper deposit is applied at a cathode current density which, generally speaking, is low but which is a high current density for the copper concentration of the electrolyte. The grain structure of the ilash deposit thus applied sets the pattern for subsequent deposits of copper substantially` independently of copper concentration of the baths and current densities employed in applying those deposits. This flash deposit of copper adheres tenaciously to the wire.

The wire then is advanced as a cathode through 3 a plating cell 26 having a high copper concentration, alkaline cyanide plating bath to apply a further deposition of fine-grained copper on the ash deposit. A high cathode current density is maintained in the cell 26 to produce a high rate of copper deposition to build up the copper deposit rapidly to a thickness sufiicient for plating thereon in subsequent acid plating baths without galvanic deposition of copper thereon. YThe wire is advanced continuously from the cell 2B through a water rinsing bath 28, and an acid bath 29 to wash off and neutralize any alkali on the wire. The wire then is advanced continuously as a cathode through acid plating cells 3l, 32, 33 and 3st, which plate copper on the previous deposit with very high current densities on the wire and very high rates of deposition.

The plating cell 24 may be constructed somewhat like that shown in Fig. 2, and consists of a conductive anode compartment 30 having slots 37-37 in the end walls thereof through which the wire l passes. A layer 38 of finely divided copper, such as scrap copper or small copper balls, rests on the bottom of the anode compartment 36, and the electrolyte employed is fed into the bottom of the compartment by means of inlet pipes 39-39. The electrolyte flows from the inlet pipes 39-39 through the layer 38 of finely divided copper, and out of the compartment 36 through the slots 37-3'1. rIihe overilow falls into an outer compartment 40 from which it flows into a suitable tank (not shown), which serves as a reservoirY from which the electrolyte is pumped through the inlet pipes 39--39.

The anode compartment 3S is connected to the positive side of a source of D. C. potential, thereby making the layer 3S of finely divided copper the anode in the cell 2t, and the anode compartment is insulated from the outer compartment 40. The nely divided copper dissolves anodioally to replenish the electrolyte with copper ions as copper is plated on the wire l0. Finely divided copper is added to the layer 3S from time to time to maintain an adequate supply of anode material. Contact sheaves S2-452, which are connected to the negative side of the D. C. source, are engaged by the Wire I0, whereby the wire is made the cathode in the plating cell 24.

The copper concentration of the electrolyte in the cell 24 is low so that a very thin, fine-grained, flash deposit of copper is applied to the wire l0. This ash deposit is pure and very fine-grained in structure due to the diluteness of copper in the electrolyte in this cell, and it is tenaciously adherent to the wire because of the purity, denseness and fine-grained structure of the deposit. The cathode current density, which is kept suiiizciently low for the low concentration of copper in the cell 24, should not be greater than about 75 amperes per'square foot, and preferably should be between about and about 50 amperes per square foot. The temperature of the bath is maintained at from about 140 F. to about 180 F.

A highly satisfactory electrolyte for use in the vcell 24 is a mixed copper-potassium cyanide electrolyte having a composition within approximately the following limits:

Oz. per gal. Copper (as cyanide) 1.5 to 3.0 Potassium cyanide (free) 0.1 to 1.0 Potassium hydroxide (free) 3.0 to 6.0 Potassium carbonate 6.0 to 7.5

The most important elements of this type of electrolyte are the copper contentand the free potassium cyanide content thereof. The pr-i ferred limits for the copper content are from 1.75 to 2.5 ounces per gallon, while the preferred limits for the free potassium cyanide content are from 0.3 to 0.7 ounce per gallon.

Negative contact sheaves l0- 46 are provided adjacent to the cell 26 which is similar to the cell 24 and includes an anode 48 composed of divided metallic copper. A heavy deposit of copper is 'applied to the wire l0 in the cell 26 to protect the wire against galvanic cell copper deposition thereon in the acid plating cells 3|, 32, 33 and 313. A deposit of from about 0.0001 inch to about 0.0002 inch is applied in the cell 26 under a substantially higher current density than was used in the cell 24. The deposit applied to the wire in the cell 26 is very negrained and dense inasmuch as the flash deposited on the wire in the cell 25 had already set the crystalline pattern of further deposits of copper.

A very satisfactory electrolyte for use in the cell 26 is a mixed copper-potassium cyanide bath having a composition within about the follow-ing limits:

Oz. per gal. Copper (as cyanide) '4.5 to 7.0 Potassium cyanide (free) 0.0 to 1.0 Potassium hydroxide (free) 3.0 to 6.0 Potassium carbonate 6.0 to 7.5

Here again, the concentrations of Vthe copper and of the free cyanide are the most important elements of theY electrolyte. The copper concentration preferably is within the range of from 4.5 to 6.5 ounces per gallon, and the free cyanide content preferably should be from 0.3 to 0.7 ounce per gallon.

The difference of potential between the contact sheaves 13E-d6 and the anode d8, the spacing of the anode from the path of the wire and the electrical resistance of the electrolyte are such that a cathode current 'density of from about 50 to about 200 amperes per square foot is maintained in the cell 26, the current density being kept substantially higher than that in the cell 20. The cell 26 is kept at a temperature of from about to about 180 F.

The wire l0 emerges from the cell 26 having a plated copper covering thereon which is sufficiently thick to protect it against galvanic deposition of copper thereon. The water rinsing bath 28 and the acid bath 29 wash off or neutralize any alkali carried by the wire from the cells 24 and 25. The acid bath 25 may be a hydrofluoboric acid solution at a concentration of from about 1.0 to about 10.0 ounces per gallon, or a suiphu'ric acid solutionv at a concentration of from about 1.0 to about 10.0 ounces per gallon, depending on the type of electrolyte employed in the cells 3i, 32, 33 and 34. The bath 25 is held at a teniperature between about 60 F. and about 100 F. Since electrolyte used in the acid plating cells 3l, 32, 33 and 35 may be a copper fiuoborate or a copper sulphate solution, if copper iiuoborate is used as the electrolyte in these cells, the hydrofluoboric acid solution is used in the neutralizing `bath 2%, whileif copper sulphate vis used in these cells, Vthe sulphuric acid Ysolution is used in the bath 29.

The wire l0 is advanced continuously through the cells 3|, 32, 33 and S vat a rate of speed between about 20 feet per minute and about 100 feet per minute, and the electrolytes in the cells Aare recircul'ated with a high degree of turbulence.

.successfully in plating copper on the conductor Oz. per gal. Copper (as fluoborate) 7.2: to 20.0 I-Iydrofluoboric acid (free) 2.5 to 8.5

The electrolyte preferably is operated at a teinperature of from about 115 F. to about 136 F., and a cathode current density of from about 500 to about 3000 amperes per square foot is preferred. A goed concentration range for these constituents is from about to about 20 ounces per gallon of copper as fluoborate, and from about 3.5 to about 6.5 ounces per gallon of free hydrouoboric acid. Good results are obtained when a cathode current density of from about 1000 to about 2500 amperes per square foot is employed.

A satisfactory sulphuric acid electrolyte for the acid plating cells will have a composition substantially as follows:

Oz. per gal. Copper (as sulphate) 7.0 to 11.0 n suiphuric acid (free) 3.0 to 6.o 05

The electrolyte preferably is kept at a teinperature of from about 60 F. to about 85 F., and the acid plating cells using this type of electrolyte preferably are operated at a cathode current density of from about 500 to about 1200 amperes per square foot. Excellent results are obtained when the copper concentration is from about 8 to about 10 ounces per gallon, the free sulphuric -acid concentration is from about 4.5 to about 5.5 ounces per gallon, and the cathode current density is from about 750 to about 1000 amperes per square foot.

The thickness of copper deposited in the cells 3|, 32, 33 and 34 in one particular example has been from about 0.003 inch to about 0.004 inch. The deposit on the wire from the acid plating cells was very fine-grained and dense, being governed by the initial pattern of the grain of the copper deposit in the cyanide cell 24, even though a cathode current density as high as about 3000 amperes per square foot was used.

The covered wire i0 is advanced from the cell 34 to a dragout recovery bath 50 having Water therein, and then through a rinsing bath 52. The Water in the bath Washes any acid on the Wire from the cell 34, and forms a dilute acid solution. This dilute acid solution is used to replace the Water that is lost from the acid cells 3 32, 33 and 34 from evaporation and other causes, and Water is supplied to replenish it, from the bath 52, if desired.

Eample I 6 feet per ininute. Triohloroethylene Was used in the degreaserl I4, and removed substantially all fats and grease from the wire. Any remaining grease and any other contaminants on the surface of the Wire were removed by a sodium orthosilicate solution at a concentration of about 5.0 ounces per gal. in the cell I5, in whichthe Wire was immersed as an anode for 18 seconds at an anode current density of 125 amperes per square foot. The Wire was immersed in the acid cleaning cell for 13 seconds as an anode at a current density of 550 amperes per square foot. The electrolyte in the cell Il was a 15% sulphuric acid solution and was maintained at a temperature of 80 F. The cell Il cleaned oxides completely from the surface of the Wire, so that it was in excellent condition for the electrodeposiv tion of copper thereon.

Each portion of the wire was immersed in the flash plating cell 24 for a period of l0 seconds at a cathode current density of 50 amperes per square foot, the period of time being just sufficient to form a thin film or ash thereon. The electrolyte was maintained at a temperature of 150 F. An alkali cyanide electrolyte having the following composition was used as the electrolyte in the cell 24:

OZ. per gal. Copper (as cyanide) 2.1 Potassium cyanide (free) 0.5y Potassium hydroxide (free) 5.0 Potassium carbonate 6.0

the cell 26 had the following composition:

Oz. per gal. Copper (as cyanide) 5.5 Potassium cyanide (free) 0.6 Potassium hydroxide (free) 5.0 Potassium carbonate 6.0

The acid neutralizing bath 29 was a 4% hydrofluoboric acid solution, and Was maintained at room temperature (about 70 FJ.

Each portion of the Wire advanced through the acid plating cells 3|, 32, 33 and 34 was immersed therein for a total period of seconds at a cathode current density of 1800 amperes per square foot. The electrolytes in these cells were held at a temperature of 128 F. A smooth, dense, fine-grained deposit 0.003 inch in thickness was formed on the wire; The electrolyte in the cells 3|, 32, 33 and 34 had the following composition:

. Oz. per gal. Copper (as fiuoborate) 18 VHydrofluoboric acid (free) 5.3

The entire deposit of copper on the Wire was uniform, nonporous, dense, tenaciously adherent and ne-grained. 'There was no treeing, and the peripheriy of the r'deposit was smooth. The temper of the steel Wire core was substantially unaffected by the electroplating operation.

l 'cell' 24 Copper" (as cyanide) 2 contindodsly'thrdugii'tiie sans and 'eensi4', is, 1s, n.118, 24, y26528,' V2,9,"3M3133;aafsuardlsz this cleaning Was'cdmpletedmthelcell' l 5, having therein an aqueous solt'in: f so'durn 'ortl'iosili- Cateat 'a 'concentration"`of "about 5 .'0 v'ounces per gallon which the vlWife was imrnesed `fr V21,8 'secondsasan anode at'a"c''rrnt density of l1`25 amprespersquar'foot. 1The wire-vlas iinsed inthe cell vl'l fr 13"se'c'nds 'asian anode fat a current density `f 550 "ar'r'iperes'fper'sqare Vfoot. The electrolyte' in `tlie"'cel1" I 1 A'vilas 'a' 15 solution of sulphuric acid, and Was'k'ept'at aternperatue V'lyte lAveas '150 F. An alkali cyanide electrolyte having the folloWingconipositiii'vvassed"infthe y O'z. :pergal :'Cop'p'er' (as'cyanid'e) @i5 Potassium nvdroxide (fre'e) 5.0

The acid .nednalinrig'tdhzs consisted Vcf a. v1o* =s1i1phurfcacidsolution,and .was 'maintained 'at atiiipzeratre`f"ab011t70 F. y

Each'pctiohof the'ivieadvanced as a cathode lthroughthe acid' plating v`(3611's '31, J3'2,k 33 arid Was iinniei'sei; in' tlie'se cells`for "a total period of 230 seconds at -a Vcathode currn'tfden's'ity of h900 ampere's per "Square foot v'arid at a bath "temperature-df "70 T11'. A mcothu-fdnn, dense. ne-

grained 'deposit :01003 inch in (thickness rtivas formed on the Wire. The electrolyte inthe `ee'lls '31, vZ-l"2,/f-Band 34* had the following composition:

vOz.perifgftl. Copper (as sulphate) 9.0 v"Sli'lphuic 'acid '(fee) 5.0

The `entire Adeposit fof fco'pper v-onthe `Wire Arwas "The faboveLdescribed methods are very v`ie'Jp'id 'land economical. They provide a 4very i'iinegrained,`dense, copper depositon 'a steelLA icle in-"a'very short period-of tune; andthe-'deposit of fcopper is uniform ltherearound. A -very `A`l'iigli -'ten'sii'e""strengthi steel Wire'ni'ay be used asthe steel core l0 Without impairing thecondit'inof anneal thereof by the 'above#liescribed' niethods, "inasmuch Yas 'the ellectroplating operations are conducted at relatively loa/temperatures These -results have been unobtainable by the use of processes heretofore known. n 4

The resulting composite Wire has a very/,high 'tensile strength, and also is electrically conductive, the conductivity ofthewire producedinaccordance with thev aboveoutlined Yspe'ciic eiia'mples -beingabout 30% of thatfof iapu're copper Wir'eof the saine size. The composite wiremay be used for communicationpurposesgand is-`eX vcellent for 'the vmanufactu're'o'f drop "wire, line 'wir-e, and other wires tvhere a V'high Itensile strength Wire having 'good conductivity tis v4required.

"While it is "possibleito /electroplate 5 heavy coatings of copper lupon-cores solelybythe use vvoi cyanide baths, the copper deposits thusioined ltend to 'be brittle,` andl cornpo'site'conductors havinga'steel cor'e provided 'with a5 heavy *copper covering deposited from cyanide fhaths'alone-are nnsatisiactory for communication purposes. -Whenthe grain pattern ofthe Vdeposit is 'established in a low copper concentration cyanide-bath in accordance with the methods described hereinabove, 'and thest'eel 'corei's protected irin -reaction Withan acid plating bathin YtheV niaiiner vdescribed hereinabove, aheavy deposit of copper may be "formedlupon'a steel core `quite rapidly by the use of an acid platin'gbath, and the "deposite `thusiorm'ed will not have the tendency 'to be brittle that is evident when a cyanide bath is 'employedto produce the copper plate.

Although in the specific embodiments-outlined hereinabove, hydrofluoboric 'acid 'and sulphuric Vacid copper .plating baths have been described, satisfactory results may be 'ob'taine'd `ivhen the 'plating'perforin'ed'in anacidbath is lcalrriedout in'other' baths that aie'acid'in nature. For example, instead of hydrfluboricac'id'orasulphuric acid bath, an acid copper plating bath 'having -as its principal cons'ttuentl'anothe'r suit- 'ableacidfsuch as sularniclacid, iiuosilicic acid, Vvacetic acid or a sulphonic acid, for example, phenolsulphonic lacid 'or benzene-di-sulphonic acid, may be used.

What lis claimed is: p

1. The'method of electroplating'copper on steel Wires, which comprises continuously advancing a steel Wire as a cathodelseriatim through an alkaline cyanide flash coating "bath containing copper dissolved thereinat 'a concentration Within the range of 'from about'l.5 to about 3l() ounces "per gallon, a Vsecond alkaline cyanide bath containing copper dissolved therein Yat a vc'firi'ce'ntration within the range of 'from about '4.5 v"to about '7.0 ounces per .gallon, vand an acid plating bath containing a still higher concentration of copper dissolved therein, maintaining inthe ycyanide'la'sh bath a cathode current Vdensity with'- in the range of from about 20 to 'about 75 arnperesper square foot for a period of ltiine sufficientto deposit a very thin'afndvery ne-grained fla-sh coating'of vcopper vvhich 'sets Va fsief pattern that causes subsequent deposits on the wire to be similarly fine-grained, maintaining in the second cyanide bath a cathode current density substantially higher than the current density in the ash coating bath to deposit a une-grained copper coating substantially thicker than the flash coating of copper, and maintaining in the acid plating bath a still higher cathode current density to form a thick copper deposit which increases materially the electrical conductivity of the resulting composite Wire.

2. The method of electroplating copper on steel wires, which comprises continuously advancing a steel Wire as a cathode seriatim through an alkaline cyanide flash coating bath containing copper dissolved therein at a concentration within the range of from about 1.5 to about 3.0 ounces per gallon, a second alkaline cyanide bath containing a higher concentration of copper dissolved therein, and an acid plating bath containing a still higher concentration of copper dissolved therein, maintaining in the cyanide ash bath a cathode current density Within the range of from about 20 to about '75 amperes per square foot for a period of time suicient to deposit a very thin and very fine-grained flash coating of copper which sets a size pattern that causes subsequent deposits on the wire to be similarly finegrained, maintaining in the second cyanide bath a cathode current -density Within the range of from about 50 to about 200 amperes per square foot to deposit a fine-grained copper coating substantially thicker than the flash coating of copper, and maintaining in the acid plating bath a stillhigher cathode current density to form a thick copper deposit which increases materially the electrical conductivity of the resulting composite Wire.

3. The method of electroplating copper on steel wires, which comprises continuously advancing a steel wire as a cathode seriatim through an alkaline cyanide flash coating bath containing copper dissolved therein at a concentration within the range of from about 1.5 to about 3.0 ounces per gallon, a second alkaline cyanide bath containing a higher concentration of copper dissolved therein, and a series of acid plating baths containing a higher concentration of dissolved copper than the concentration in the second a1- kaline cyanide bath, maintaining in the cyanide flash bath a cathode current density Within the range of from about 20 to about '75 amperes per square foot for a period of time sufficient to de-n posit a very thin and very fine-grained flash coating of copper which sets a size pattern that causes subsequent deposits on the Wire to be similarly fine-grained, maintaining in the second cyanide bath a cathode current density Within the range of from about 50 to about 200 amperes per square foot to deposit a ne-grained copper coating substantially thicker than the iiash coating of copper, and maintaining in the acid plating baths a cathode current density Within the range of from about 500 to about 3000 amperes per square foot to form a series of increments of a thick copper deposit which increases materially the electrical conductivity of the resulting composite Wire.

4. The method of electroplating copper on steel Wires, which comprises advancing continuously a steel Wire as a cathode seriatim through an alkaline cyanide, grain-pattern-setting bath having copper dissolved therein at a concentration within the range of from about 1.5 to about 3.0 ounces per gallon, an alkaline cyanide plating bath having copper dissolved therein at a concentration from about 4.5 to about 7.0 ounces per gallon and an acid plating bath having copper dissolved therein at a high concentration, maintaining a current density on the portion of the wire in the grain-pattern-setting bath within the range of from about 20 to about *'75 arnperes per square foot and for such a period of time as to just form a very thiniinegrained, copper, hash deposit on the wire, maintaining a current density on the portion of the Wire in the cyanide plating bath within the range of from about 50 to about 200 amperes per square foot to form a fine-grained copper deposit on the ash deposit to protect the Wire against galvanic action in the acid plating bath, and electroplating a heavy deposit of copper on the secondmentioned deposit in the acidplating bath ata high cathode current density.

5. The method of electroplating copper on steel wires, which comprises advancing continuously a steel Wire as a cathode seriatim through an alkaline cyanide, grain-pattern-setting bath having copper dissolved therein at a concentration'y of about 2.1 ounces per gallon, an alkaline cyanide plating bath having Vcopper dissolved therein at a concentration of about 5.5 ounces per gallon and an acid plating having copper dissolved therein at a very high concentration, causing an electric currentv of such magnitude to now through the grain-pattern-setting bath that the current density on the portion of the wire in that bath is from about 20 to about '75l amperes per square foot whereby a very thin, fine-grained, copper ash deposit is formed on the Wire, causing an electric current of such magnitude to now through the cyanide plating bath that the current density on the portion of the wire in that bath is from about 50 to about 2,00 amperes per square foot to forma fine-grained copper deposit on the hash deposit, and electroplating a heavy deposit of copper on the second-mentioned deposit in the acid plating bath at a very high cathode current density.

6. The method of electroplating copper on steel wires, which comprises advancing continuously a steel Wire as a cathode seriatim through an alkali cyanide grain-pattern-setting bath having copper dissolved therein at a concentration from about 1.5 to about 3.0 ounces per gallon, through an alkali cyanide plating bath having copper dissolved therein at a concentration of from about 4.5 to about '7.0 ounces per gallon and through an acid plating'bath having copper dissolved therein as copper fluoborate at a copper concentration of from about '7.2 to about 20.0 ounces per gallon, causing to iiow through the grain-pattern-setting bath an electric current of such magnitude that the current density on the portion of the Wire in that bath is from about 20 to about 75 amperes per square foot and for such a period as to form a very thin, negrained, copper, flash deposit on the wire, causing to now through the cyanide plating bath an electric current of such magnitude that the current density on the portion of the wire in that bath is from about 50 to about 200 amperes per square foot to form a protective, une-grained,

copper deposit on the nash deposit, and electro-A plating a heavy deposit of copper on the secondmentioned deposit in the acid plating bath at a cathode current density of from about 500 to about 3000 amperes per square foot.

7. The method of forming an electroconductive layer of copper onsteel wires, which com- 11 prises-advancing asteeI-Wire continuously-as a cathode 4through a Acyanideiiashbatlti `containing fromabout 1.575 to-about12.5 ounces pergallon ofcopper as cyanide4 and `from about y0.3 to `GJ'I ounce per gallon .Y ois free potassium cyanide, through a'cyanide plating bathv containing from about 4.5 to 6.5ounces pergallon of copper as cyanide and from about 0.3 to 0.7 ounce pergallon--ofiree potassium -cyanide,and then through anv acid plating bathrcontaining from about l5 toLZ-ounces per gallon ofcopper asluoborate and-"from about 3.5to about-6.5 ounces pergallonv of free hydrofluoboric acid, electroplating eachincrement off .the vvire` passing through the cyanide flash bath-ata vcathode current density offrom about -20 to vabout-Zvamperes per square footfor afperiod suiiicient to vform only athin-, fine-grained, flashldeposit on the-wire, velectroplating each incrementY of-Y the Wire` passing through. .the cyanide ...plating bath ata` cathode currentdensity offfromaboutfof to abouty 200 amperes persquare foot .for alpreriod sunicient to form a fine-grained, protective` deposit of. copper on the ash deposit`,,andelectroplating eachincrement of tl'i'evwire passing.` through: the acid platingY bath'wat La cathode Ycurrent density,V of at least. 500 amperesvper Ysquare Yfoot for a Vvperiod sufficient to form a1 deposit `of copper on. the protective deposit sufciently thickrto. materially increase the .electrical conductivity.u of the resultigcomposite Wire.H

8." yThe method of electroplatingcopperon steel Wires, .which comprises advancing.Y continuously a'st'e'el .wire .asia/cathode seriatirnv through -a lcyanide.- grain-pattern-setting bath. havingY copper' dissolved-therein -as Fcyar-iide Y at a-concentration of-2L1Hounces of copperfper'gallon, free potassium cyaniderat a concentration off 0.5v ounce per gallon, free potassiumihydroxide at a concentraticn off-5.0 ounces yper gallon andpotassium carbonate. at 4aconcentration of 6.0- ounces'- per gallonf. throughV a cyanide.` plating: bath having copper dissolvedfthereinias cyanide atta-copper concentration of 5.5 ounces pergallon; free potas-v sium-cyanide atE a`concentration Iof '0.6f ounce per gallonffree` potassium-hydroxideV at a concentrationot 5.0-'ounces per'gallon and potassium*v car bonate'atfa` concentration of- 6.0 founces pergallon; andv through an acid lplatingA bath having copper dissolved tthereinas copperfluoborate" ata copper concentration of 18.1'ounces I of s' copper -per gallon; and free. hydrofiuoborio acidvl atg. concentration ofaboutvounces perrgallon; electropl-ating. each portion -oir the' Wire in: the-fgrain-pattern-setting bathfor. about 10. seconds atT a current" density of: about- 50 vamperesA per squarci" foot wherebyy a very thin;` fine-grained; coppery fl'ash deposit' is formed-V on' the'v Wire, electroplatin'g each y portion of theiwire inthe cyanidefplating-bath'fori about 40'4 seconds at a;- current' densityv4 of about 100 amperes per= square' foot toform alfinelgrained' copper depositen theashdeposit, and electroplating-feachiportion-iofftlie Wireirl-thef acidplatl ing bath fori'aboutilflsecoiidsata current density:- of.` aboutv 1'800' anlperesflper` sduar'ef foot to" form a-heavyfdepositof" copper on th'e'ls'e'cond-VV mentionedv deposit".

9;- Themethod 'ofele'ctroplatin'g copper' onsteel Wires;Y which comprises' advancing.y continuously al steel. wire as ai cathodey seriatini through an alk'alinefc'yanidegrainipattern-setting bath havin'g copper dissolved'thereinffat a-concentiiation of from abouti-15"' to"y about' ounces per gallon, thruglfrian'. alkaline? cyanide plating bath having copperr dissolvecttherein at a* concentration of' from about 4.5 to-.abouh 7.0`1 .ounces..per., gallon and through -a-.sulphuriceacid lplating... bath uhav.- ing ,copper dissolved .therein at aconoentration of from-about V7.0 to-about.11.0 ouncespergal-A lon, maintaining a low-current density on the portionfof kthe Wire .in the grain-pattern-setting bath for such a period of time asV to form on the Wire avery thin, fine-grained, copper, flash deposit, maintaining ahigher current densityv on the portion -of.th.e:wire-.in the cyanide plating bath for such a periodofntime as to form on the Wire a fine-grained copper 1 deposit' on-:therash deposit to protect the wireagainst galvanicdeposition in the acid -plating-sbath, and electroplating a heavyV deposit of.copper.on.the second.- inentioned deposit in the'gsulphuric-:acid plating bath at a cathode-current.' density of .from about 500 to about lamperespersquare` foot.V

10. The method ofY .electroplating l. af conductive layer of. copper.y on steel Wires, which :comprises advancing a steel Wire-continuouslyas fa cathode through a cyanide.V iiash.A bath containing. from about 1.75 toabout;2.5.;ounces per-gallonof cop-v per-as cyanideand from about 0.3 toifounce per gallon of free potassium'- cyanide, through .ya cyanide plating bathfcontainingrom about-4:5 to 6.5 ounces per gallonoficopperiasfcyanide-and from about 0*.3 .to 0.57 Iounce` per-.gallon .oifree poftassium cyanide,I and .then :through .an acid-.plating bath containing fromlaboutfetoaboutzflO ounces per gallonof coppenassulphate and froml about f1.5 to about.5;5/ouncesnperl gal-lon of. free sulphuric acid, electroplatingf each Aincrement `of the Wire passing :through :thefashecyanidefbath at a cathode currentxdensity-'of-from ab0ut20'to about 75 amperes :per` square: foot for4 a-period suicient to form fonly -a-i thin, line-grained, flash deposit on the Wire, electroplating eachv increment of theWiref-passing throughthe'cyanide plating bath at -acathode current densityv of from about 50to .about -Y 200 4amperesffper4v square foot for a periodf-suicient'to formar line-grained, protective deposit of copper onfthe asn deposit, and v electroplating: each increment ofy ther Wire passing through the' acid plating: bath at aV cath.- ode current density-otatcleast 500 amperesx-per square foot 'for 'aperiod'suicient to -form afdeposit of copper onrtheM protective deposit suf-l iiciently thick` to ltflaterially,fincrease'thev electrioalA conductivity of` the resulting' composite wire.

l1. The: method', of electroplating. copper.V onr steel wires, Whichfcomprisesfadvancing continue ously a steel Wirerasl'ai cathodezseriati'm through a cyanide grainepatternlsetting 'bathhavin'gcopa per dissolved therein as'cyanide ata:` copper concentration of 2.11.ouncesfpergallon; free potassium cyanide atfa'.A concentration= of 0.5 ounceper gallon, free potassiulnhydroxide at a` con" centr-ation of 5.0. ounces'per gallon and potas-l sium carbonatefat'a concentration'ofiGlO ounces per gallon,through-a' cyanide plating bath having copper'dis'solvedltherein asrcyanid-e at a copper .concentration-'fof about- 555 `ouncesA per' gallon, freepota'ssiumcyanid ataconcentration of 0.6 ouncel per' gallon",freepotassiurn hydroxide at a concentration of-f51`0 ounces: per Agallon and potassium carbonate at a concentration of 60` ounces per gallon, andV through a sulphuric aoidplating bath having copper dissolved thereinlascopperv sulphate at a copper concentration of`9.0 ounces per gallon and freesulph'uric'acid' at a concentration of l5.0 ounces per" gallon, maintaininginA the fgrain-pattern-se'tting bath a'Y cathode* current density of5'0`ampe're'spersquare footfor'a period of 10 seconds to form on the wire a very thin, fine-grained, copper, flash deposit, maintaining in the cyanide plating bath a cathode current density of 100 amperes per square foot for a period of 40 seconds to form on the Wire a fine-grained copper deposit on the flash deposit to protect the Wire against galvanic deposition in the acid plating bath, and maintaining in the acid plating bath a cathode current density of 900 amperes per square foot for a period of 230 seconds to form a heavy deposit of copper on the second-mentioned deposit.

GUY E. MURRAY.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,317,350 Adler et al. Apr. 27, 1943 2,420,291 Adler May 13, 1947 OTHER REFERENCES Transactions Electrochemical Society, Modern Electroplating (special volume), 1942, pp. 155-158, 173-175, 177-178, 186-187.

Transactions Electrochemical Society, vol. 88,. 1946, pp. 263-266. 

1. THE METHOD OF ELECTROPLATING COPPER ON STEEL WIRES, WHICH COMPRISES CONTINUOUSLY ADVANCING A STEEL WIRE AS A CATHODE SERIATIM THROUGH AN ALKALINE CYANIDE FLASH COATING BATH CONTAINING COPPER DISOLVED THEREIN AT A CONCENTRATION WITHIN THE RANGE OF FROM ABOUT 1.5 TO ABOUT 3.0 OUNCES PER GALLON, A SECOND ALKALINE CYANIDE BATH CONTAINING COPPER DISSOLVED THEREIN AT A CONCENTRATION WITHIN THE RANGE OF FROM ABOUT 4.5 TO ABOUT 7.0 OUNCES PER GALLON, AND AN ACID PLATING BATH CONTAINING A STILL HIGHER CONCENTRATION OF COPPER DISSOLVED THEREIN, MAINTAINING IN THE CYANIDE FLASH BATH A CATHODE CURRENT DENSITY WITHIN THE RANGE OF FROM ABOUT 20 TO ABOUT 75 AMPERES PER SQUARE FOOT FOR A PERIOD OF TIME SUFFICIENT TO DEPOSIT A VERY THIN AND VERY FINE-GRAINED FLASH COATING OF COPPER WHICH SETS A SIZE PATTERN THAT CAUSES SUBSEQUENT DEPOSITS ON THE WIRE TO BE SIMILARLY FINE-GRAINED, MAINTAINING IN THE SECOND CYANIDE BATH A CATHODE CURRENT DENSITY SUBSTANTIALLY HIGHER THAN THE CURRENT DENSITY IN THE FLASH COATING BATH TO DEPOSIT A FINE-GRAINED COPPER COATING SUBSTANTIALLY TICKER THAN THE FLASH COATING OF COPPER, AND MAINTAINING IN THE ACID PLATING BATH A STILL HIGHER CATHODE CURRENT DENSITY TO FORM A THICK COPPER DEPOSIT WHICH INCREASES MATERIALLY THE ELECTRICAL CONDUCTIVITY OF THE RESULTING COMPOSITE WIRE. 